https://duckduckgo.com/?q="Arbennig%3AAboutTopic"+site%3Acy.wikipedia.org (https://archive.fo/P2fop ) returns a slate of "Page unavailable", for instance https://cy.wikipedia.org/wiki/Arbennig:MobileLanguages/17 which says
This page is not available on desktop. Please click the mobile view link at the bottom of the page.
but returns a status code 200 and contains an inappropriate
<link rel="canonical" href="https://cy.wikipedia.org/wiki/Arbennig:MobileLanguages/17"/>
In such a case, the special page should either
- return 404, or
- return 302 and redirect to the Wikidata item.
Additionally, the canonical URL should be something with actual content.